A typical acoustic ceiling tile is a non-woven structure including a core manufactured from base fibers, fillers, and binders. The base fibers are usually mineral wool or glass fibers. The fillers are commonly perlite, clay, calcium carbonate, or cellulose fibers. The binder is typically cellulose fibers, starch, latex, or similar materials. Upon drying, the binder forms bonds with the other materials to form a fibrous network that provides structural rigidity to the core. To be used as a typical ceiling tile, the core should be substantially flat and self-supporting in order to be suspended in a typical ceiling tile grid or similar structure.
For non-woven structures to be suitable for acoustical ceiling tile applications, they generally satisfy various industry standards and building codes relating to fire rating and noise reduction. For example, industry standards typically specify ceiling tiles to have a Class A fire rating according to ASTM E84, which generally requires a flame spread index less than 25 and a smoke development index less than 50. Regarding noise reduction, industry standards typically specify the acoustical ceiling tile to have a noise reduction coefficient according to ASTM C423 of at least about 0.55.
Acoustic ceiling tiles are commonly formed via a wet-laid process that uses an aqueous medium to transport and form the tile components into a non-woven mat used to form the core of the acoustic ceiling tile. The basic process involves first blending the various tile ingredients into an aqueous slurry. The aqueous slurry is then transported to a headbox and distributed over a moving, porous wire web to form a uniform mat having a desired size and thickness. Water is then removed and the mat is dried. The dried mat may then be finished into the ceiling tile structure by slitting, punching, coating and/or laminating a surface finish to the tile. In the wet-laid process, water serves as the transport media for the various tile ingredients. This wet laid process is acceptable because high production speeds can be attained and because low cost raw materials (for example, recycled newsprint fibers, recycled corrugated paper, scrap polyester fibers, cotton linters, waste fabrics, and the like) can be used. However, using water to manufacture acoustical ceiling tile presents a number of shortcomings that render the process and formed product less than desirable.
The wet-laid process uses a great deal of water to transport and form the components into the ceiling tile structure. The large amounts of water must eventually be removed from the product. Most wet processes, therefore, accommodate water removal by one or more steps of free draining, vacuum, compression, and/or evaporation. These process steps entail large energy demands to transport and remove the water. As such, the handling of large volumes of water to form the tile along with the subsequent removal and evaporation of the water renders the typical wet-laid process relatively expensive due to high equipment and operating costs.
It also is difficult using a wet-laid process to form an acoustical ceiling tile having high sound absorption properties. In a wet-laid process, the formed ceiling tiles tend to have a sealed surface due to the nature of the ingredients in the wet-laid formulation. A ceiling tile with a sealed surface generally has a less efficient acoustical barrier because the tile is less porous, which renders the tile less capable of absorbing sound. The sealed tile surface may actually reflect sounds, which is an undesired characteristic in an acoustical ceiling tile.
These undesired acoustical characteristics are believed to occur from the hydrophilic nature of the tile ingredients typically used in the wet-laid process. Cellulose fibers (for example, recycled newsprint), which are commonly used as low cost binder and filler in a ceiling tile, are highly hydrophilic and attract an extensive amount of water. Due in part to such hydrophilic components, wet-laid tiles typically have a high tipple moisture content (i.e., the moisture level of the board immediately prior to entering the drying oven or kiln) of about 65 to about 75 percent, which increases the demands of evaporation during drying. As a result, a high surface tension is generated on the tile ingredients during drying as water is removed from these hydrophilic components. Water, a polar molecule, imparts surface tension to the other components. This surface tension generally causes the tile surface to be sealed with a less porous structure. It is believed that the surface tension draws elements in the tile closer together densifying the structure and closing the tile pores in the process. Consequently, wet-laid produced ceiling tiles require further processing to perforate the tile in order to achieve acceptable noise reduction. Therefore, while a wet-laid process may be acceptable due to increased production speeds and the ability to use low cost materials, the use of water as a transport media renders the process and resulting product less cost effective when acoustic characteristics are required for the product.
In some cases, a latex binder also may be used in acoustical ceiling tiles and is often preferred in a wet-laid process using mineral wool as the base fiber. Latex, however, is generally the most expensive ingredient employed in a ceiling tile formulation; therefore, it is desired to limit the use of this relatively high cost ingredient. Other binders commonly employed in ceiling tiles are starch and, as described above, cellulose fibers. Starch and cellulose, however, are hydrophilic and tend to attract water during processing and generate the high surface tension problems described above.
Other non-woven structures, such as diapers, hygienic wipes, filtration media, and automotive insulation, may be formed via an air-laid process that uses air as the transport media for the various ingredients forming a non-woven material. An air-laid process eliminates the need to transport and remove water; however, all components in the formulation must be transportable in an air stream. As a result, heavy, dense, or long fibers as well as liquid components are generally not suitable for the air-laid process. That is, liquid resin binders and/or latex binders commonly used in ceiling tile manufacture generally cannot be used in the air laid process. Typical air-laid processes, therefore, prefer short glass fibers employed as the base fiber (i.e., about 10 mm in length) together with some type of heat-fusible or thermal bonding fiber, such as a single component or a bi-component bonding fiber. Once formed into a non-woven material, the thermal bonding fiber is heated to melt a portion of the fiber in order to bond the base fiber structure within the desired core structure.
WO 2006/107847 A2 discloses an air-laid process to form automobile insulation and ceiling tile structures using bi-component thermal bonding fibers and synthetic or cellulose matrix fibers. In one example, the '847 publication describes a ceiling tile composition of 30 percent bi-component fiber and 70 percent cellulose fiber (fluff) that provides improved acoustical properties over commercial mineral fiber and glass fiber ceiling tiles. While providing improved acoustical properties, the disclosed ceiling tile structures of the '847 publication have the shortcoming that they would generally not comply with current fire code ratings specified by industry standards for use as a ceiling tile. With the use of 70 percent cellulose fibers in the ceiling tile (as well as 100 percent organic fibers), it is expected that the formed base mats of the '847 publication would not comply with the fire code ratings of ASTM E84 requirements for ceiling tiles due to such high levels of cellulose and organic fibers.
The '847 publication above and US 2006/0137799 A1 further suggest that non-woven structures can be made using air-laid processes with glass fibers together with bi-component fibers. While the glass fiber would provide enhanced fire ratings under industry standards, glass fibers having a short size suitable for air-laid processes are a more expensive raw material and have health and environmental disadvantages relative to other raw materials. For example, glass fibers may cause irritation to human skin, eyes, and respiratory systems. Many organizations consider glass fibers as an acute physical irritant to skin, eyes, and the upper respiratory tract. Generally, the smaller the fiber sizes, the harsher the irritation. In some cases, if the exposure to glass fibers is sufficient, the fibers may produce irritation dermatitis and difficulty in breathing. In other cases, some studies have shown that fiberglass when combined with dust, dirt, and moisture can be a good medium for microbial growth of mold, fungus, and some bacteria.
As noted above, mineral wool also is commonly used in acoustical ceiling tiles to provide enhanced fire ratings because mineral wools can have melting points up to 2200° F., which is even higher than common glass fibers. Mineral wools are commonly used in the wet-laid process along with starch or latex binders to form acoustical ceiling tiles. However, due to the abrasive nature and high shot content of typical mineral wools (i.e., up to about 60 percent in some cases), this raw material is generally not recommended for use in an air-laid process because the abrasive nature of the mineral wool fiber tends to be destructive to the air-laid forming equipment and the high shot content can plug air filtering systems to decrease the efficiency of vacuum suction boxes. With decreased vacuum strengths, the air-laid forming head has difficulty forming a uniform mat having a basis weight sufficient to provide the rigidity needed for ceiling tiles. As used herein, mineral wool shot generally refers to a by-product of the mineral wool manufacturing process comprising non-fibrous, mineral particulate matter having diameters ranging from about 45 to about 500 microns.
The '847 publication lists glass fibers and ceramic fibers as suitable synthetic matrix fibers to be used in an air laid process, but specifically does not list mineral wool as an acceptable substitute. As generally understood, mineral wool fibers are considered distinct from glass fibers and ceramic fibers. Even though all such fibrous types are generally man-made or synthetic fibers, each has different characteristics and properties due to raw material sources and manufacturing methods. Glass fibers are manufactured through an extrusion process forming a continuous filament that is typically chopped into a desired size; as a result, glass fibers typically do not include an appreciable shot content. Ceramic fibers, on the other hand, are typically made from a spinning or blowing method with more expensive raw materials. Ceramic fibers typically have substantially less shot content than mineral wool fibers.
Notwithstanding the above, however, due to the strength of the high melting component in common bi-component fibers used in air-laid forming processes, existing multi-component fibers also have a relatively high strength (i.e., break load and elongation), which is a property desired in the products for which this type of fiber is commonly used (i.e., diapers, hygienic wipes, filtration media, and automobile insulation). However, consumers of acoustic ceiling tile expect the tile to be manually cuttable, such as with a common utility knife, so that an installer can easily cut holes in the ceiling tile for sprinklers, lights, HVAC ducts, and the like. In addition, it is not uncommon for a typical suspended ceiling to require partial size tiles for edges or corners. Because acoustic ceiling tiles generally come in standard, fixed sizes, the installer is often required to cut individual tiles to fit the particular requirements of the ceiling grid. Generally due to the high strength (i.e., break loads and elongation) of commercially available bi-component fibers, forming acoustic ceiling tiles using existing bi-component fibers produces a tile that requires excessive force to cut and exhibits fiber pull out, which are properties undesired by consumers and installers.
In short, existing wet-laid and air-laid processes with available ingredients commonly used therewith cannot cost effectively produce an acceptable acoustic ceiling tiles that meet all industry and building code standards (i.e., acoustic requirements) as well as consumer expectations for acoustic ceiling tiles (i.e., cutability, flatness, self supporting, and the like). Existing wet-laid processes are energy and capital intensive and form ceiling tiles with less desired acoustical properties. Air laid non-woven materials, which may be suitable for diapers, filter media, and automotive insulation, may be more economical to manufacture, but existing formulations and processes are not suitable to manufacture acoustic ceiling tiles meeting both consumer and industry specifications. Air laid non-woven materials formed with high amounts of cellulose and/or organic fibers generally will not meet industry fire rating standards for ceiling tiles, and the use of available bi-component fibers renders the formed material difficult to cut due to the high strength and elongation of these fibers. While short glass fiber can be use in ceiling tiles and an air-laid process, glass fibers can be cost prohibitive and have health and environmental concerns.
Accordingly, a flat, self-supporting non-woven material comprising bi-component fibers and method of making thereof that is suitable under industry standards as acoustic ceiling tile (i.e., acoustic properties) that can be fabricated without the energy and capital costs of a wet-laid process and that also meets consumer expectations for cutability are desirable.